Executing applications deployed from remote sources can be dangerous. Applications from remote sources may contain malicious code like worms or viruses that can damage or misuse a user's computer or information.
To partially combat this problem, typical Internet browsers can execute an application published to a remote location (e.g., an Internet domain) with a trust level predetermined for that location. Applications executed at a high trust level are permitted to perform riskier operations than those executed at a low trust level. Trust levels used by these Internet browsers are typically set prior to running the application based on how trustworthy the remote location is deemed to be. To execute applications with these Internet browsers, however, a user typically must have access to the remote location, such as via the Internet.
If a user wants to execute an application published to a remote location for later use when he or she will not have remote access, the user can save the application onto his or her local machine. The user can then later execute the application when he or she does not have remote access. There is a significant danger in doing so, however. The application may not execute at an appropriate trust level when executed from the user's local machine. This is because applications loaded from a local machine typically execute with a higher trust that is assigned to the local machine.
Similarly, if a user wants to execute an application that is not published to—but does originate from—a remote location, the user can save the application onto his or her local machine. The user can then execute the application but it may execute at an inappropriate trust level. One common example of this is when applications are received via email or floppy disk. While the user can run these applications, to do so the user typically saves the application to his or her local machine, often implicitly granting the application a higher trust level than it deserves.
In these and other cases where an application is received from a remote source and saved locally, the trust level at which the application is executed can be too high or too low. This is because many computer systems assume a particular level of trust (usually too high) for applications cached or executed from a local source. This potentially endangers a user's computer and, importantly, personal or corporate information.
Assume, for example, that Joe emails Jane an application and Jane saves the application onto her local machine. By so doing Jane can execute the application from her local machine. When Jane executes the application from her local machine, however, her computer typically assumes a trust level based on the location from which the application was executed (locally), which is often inappropriate. If the application contains malicious code, when Jane executes the application from her local machine it may damage her computer, steal information, and the like.
Similarly, if Jane saves locally an application from a website and later executes it, the application is typically granted too high a trust level. If it is granted too high a trust level the application is executed at the higher, inappropriate trust level, thereby endangering her computer and its information.
Further, even if the application Jane runs is not given too high a trust level, but just a different trust level than that at which it will optimally execute, the application may perform inconsistently or otherwise operate poorly.
Thus, typical trust levels granted in executing applications locally that originate from remote sources are often too high or too low, either potentially endangering a user's computer or sacrificing consistent and/or robust operation of the application.